Seal for discharge lamps



July 5, 1938. J. w. MARDEN ET AL 2,123,015

SEAL FOR DISCHARGE LAMPS Filed April 1, 1936 INVENTOR J 14/. MJFDf/V 6'.NE/Ji' F.

ATTORNE Patented July '15, 1938 UNITED STATES PATENT OFFICE- SEAL FORDISCHARGE LAMPS John Wesley Marden, East Orange, and George Meister,Newark, N. J., assignors, by mesne assignments, to Westinghouse Electricand Manufacturing Company, East Pittsburgh, Pa... a corporation ofPennsylvania Application April 1, 1936, Serial No. 72,048

5 Claims.

Our present invention relates to seals for electric apparatus andparticularly electric discharge apparatus wherein a discharge occursbetween two electrodes in a gaseous atmosphere under comparatively highpressure. In the prior art various types of seals have been employedwherein the leading-in conductors for supplying the electrical energy tothe electrodes or filament within the envelope are sealed through theVitreous envelope. Moreover the problem of providing a seal such thatthe coemcient of expansion of the metallic leading-in conductorapproximates that of the vitreous envelope so as to pre-- vent crackingof the seal with attendant loss of the vacuum or gaseous medium has longbeen recognized.

The customary construction has been to provide the leading-in conductorwith a section of a metal having an analogous co-emcient of expansion tothat of the vitreous envelope with the remainder of the leading-inconductor being of a less expensive metal or of a refractory metalcapable of withstanding high temperatures due to heating of theelectrode or filament. However, with such construction that portion ofthe leading-in conductor having the desired, co-eificient of expansionhas limited to a considerable extent the current carrying capacity ofthe leading-in conductor.

In instances where the electric discharge device comprises a vitreousenvelope provided with oppositely disposed electrodes between which adischarge occurs the electrodes are either heated to a thermionicemission from an exterior source or the electrodes are thermionically'heated by the discharge occurring between theeIectrodes upon theapplication of electrical energy thereto.

In addition the envelope is usually provided with a gaseous mediumcomprising a metallic vapor, such for example as sodium, cadmium,mercury or the like at a substantial pressure ranging from a fewmillimeters of mercury to several atmospheres. Moreover as the pressureof the gaseous medium normally increases with increase of temperaturethe provision of a suitable seal for the leading-in conductors presentsan even more momentous problem than is present with the usualincandescent lamp or electric device utilizing a vacuum.

We have previously shown and described in our copending applicationSerial No. 49,448, filed November 13, 1935, that the maximum efllciencyof a high pressure mercury vapor lamp is dependent on the maximumwattage per centimeter of arc length. In order to obtain maximumefficiency comparatively high currents must be impressed upon theelectrodes which necessitates leading-in conductors for the device notonly capable of carrying the necessary currents, but in additional suchcharacter as to form a perfect,

seal so that the high temperatures of operation of the device will notdestroy the seal formed at the juncture of the leading-in conductors forthe electrodes with the vitreous envelope.

It is accordingly an object of our present invention to provide a novelseal for electric devices particularly of the high pressure typeemploying a gaseous medium wherein the leading in conductor forms anintegral seal with the vitreous envelope of the device which will not bedetrimentally aliected by the high temperatures of operation of thedevice nor by the high pressure of the gaseous medium contained withinthe envelope.

Another object of our present invention is the provision of a seal for avitreous envelope or container wherein the leading in conductor issealed to the envelope in such manner as to provide an integral sealcapable of withstanding the high temperatures and pressures of operationof the device and of carrying the requisite electrical currents duringoperation.

Another object of our present invention is the provision of a seal for avitreous envelope or container wherein the leading in conductor isprovided with a portion formed of thin metal having a high melting pointand due to its crosssectional area forms an integral seal with theenvelope without the necessity of the seal forming portion being of thesame coefficient of expansion as that of the envelope.

Still further objects of our present invention will become readilyapparentto those skilled in the art by reference to the accompanyingdrawing wherein,

Figure l is a fragmentary view in cross-section of an electric dischargedevice particularly of the high pressure metal vapor type provided witha seal constructed in accordance with our present invention.

Figure 2 is an enlarged cross-sectional view taken on the line 11-11 ofFig. 1.

Figure 3 is a perspective view on an enlarged scale of a seal forelectric discharge devices 0011- employing seals in accordance with theteachings of our present invention.

Referring now to the drawing in detail we have shown in Fig. l avitreous envelope I constructed of hard glass, silica, or the like, butin instances where the device is of the metallic vapor type which issubjectable to high temperatures of operation it is preferable toconstruct the container or envelope I of quartz due to its high meltingpoint. The envelope I is provided with a tubular extension I formedthereon during the sealingin process and embedded in the tubular portionis a leading-in conductor forming an integral seal with the tubularextension portion of the vitreous container or envelope. Theconstruction of this leading-in conductor may be better appreciated byparticular reference to Fig. 3 wherein the leading-in conductorcomprises a substantially cylindrical member 'I. This member may beformed of any suitable thin metal, such as tungsten, tantalum, butpreferably molybdenum foil of about 1 mil thickness. This metal isformed into the configuration of a cylinder by rolling and joining theoverlapping ends and securing the same in any suitable manner, such asby welding I.

The cylindrical metallic foil member I is provided with a longitudinalslot 9 for a purpose to be hereinafter more fully described andconnected to this member 1 in any suitable manner, such as by welding,is an electrode III of suitable refractory metal, such as tungsten,which may be provided with an additional refractory metal layer ofcoiled tungsten I2 with this portion being subjected to the dischargebetween the oppositely disposed electrodes during operation of thedevice.

Also connected to the cylindrical metallic foil portion is a rod likeportion or wire II which may be formed of substantially U-shapedconfiguration having its ends secured as by welding to the metallic foilportion with the remaining portion of the wire II joined in a similarmanner to the base of the U-shaped portion and constituting that portionof the leading in conductor adapted to be disposed exteriorly of thecontainer or envelope I asshown more clearly in Fig. 1. Prior toconnection of the exteriorly disposed portion II of the leading inconductor a core of vitreous material ll of the same composition as thatof the vitreous envelope I is inserted in the cylindrical metallic foilportion I of the leading in conductor thus conditioning the same forsealing in to the envelope of the discharge device. This latter step maybe accomplished in any suitable manner, but we find it expedient toemploy the method and apparatus shown more particularly in Fig. 4.

As the spacing between the electrodes of a discharge lamp of the metalvapor type is an essen tial factor in its efficiency of operation wefirst join the envelope I to a suitable vitreous chamber II and providethe opposite end of the envelope with a tubular member II having anelbow or the like II.

The lower leading-in conductor as viewed from Fig. 4, together with itselectrode and seal forming portion, as shown more particularly in Fig.3, is then inserted into the chamber II while its upperend is open andsuch leading-in conductor slid downwardly of the chamber II and envelopeI until the extremity of the leading-in conductor rests against theshoulder portion II thus accurately positioning the leading in conductorand electrode within the lower portion of the envelope I preparatory tothe sealing in operation.

Next the upper leading in conductor together with its respectiveelectrode and seal forming portion is inserted into the chamber lIandmoved I downwardly of the chamber II until the upper electrode ispositioned the desired distance from the lower electrode.

the upper electrode and leading-in conductor in this desired position.

The vacuum pump (not shown) which is connected to the chamber II is thenoperated to evacuate the envelope I and the lower portion of theenvelope I is suitably heated by flames II until the envelope attains asuitable fusing temperature and at the same timethe vitreous core II- ofthe leading in conductor is also heated to the fusion pointresulting incomplete fusion of the core II with the envelope I both above and belowthe cylindrical metallic foil portion I and also fusion of the core I land envelope I occurs through the longitudinal opening I provided in thecylindrical metallic foil section I until complete fusion of the core IIand envelope I results. thus completely embedding the leading-inconductOr and particularly the cylindrical metallic foil portion I inthe tubular portion I formed on the envelope I'during the fusion to forma complete integral seal with the envelope.

After the desired degree of evacuation of the envelope I is obtained andthe appropriate gaseous medium or vapor forming metal is introduced intothe envelope I the flames I! are moved adjacent the upper seal formingportion where the same operation is performed to form the upper integralseal between the envelope I and the leading-in conductor particularlythe cylindrical metallic foil portion 1. The envelope I and portions IIof the leading-in conductor are then severed from the chamber II andtubular member II thus completing the device.

It thus becomes obvious to those skilled in the art that we haveprovided a leading-in conductor particularly adaptable to electricdischarge devices subjectable to extremely high temperatures andpressures during operation wherein the leading-in conductor forms anintegralseal with the vitreous envelope. Moreover, the seal formingportion being of comparatively thin metal or foil facilitates theradiation of heat which is generated by the resistivity thereof to thepassage of the electric current thus obviating possibilities of crackingof the seal. While preferably the seal is formed of a metal having acoefllcient of expansion simulating that of the vitreous envelope itneed not necessarily have such precise coemcient of expansion due to itsbeing of comparatively thin cross section. In addition the area ofcross-section of the cylindrical metallic foil portion of the leading-inconductor is such that the requisite electrical current can be readilysupplied to the electrodes without danger of overheating.

Although we have shown and described one specific embodiment of ourinvention we do not desire to be limited thereto as various othermodiflcations of the same may be made without departing from the spiritand scope of the invention as set forth in the appended claims.

What is claimed:

1. The combination of a vitreous container, a conductor fused to aportion of said container comprising a cylinder of metal foil, aleadingin conductor secured to the wall of said cylinder and extendingexteriorly of said container, and an electrode within said containerhaving its The open end of the chamber II is then sealed as shown at IIto thus hold ends connected to the periphery of said cylindricalconductor and extending a substantial distance on the surface thereof inthe direction of the longitudinal axis of said cylinder to form asupport for said electrode.

2. The combination of a discharge device provided with an envelope ofvitreous material, leading-in conductors comprising substantiallycylindrical members formed ofmetal foil having their interior andexterior surface fused to said envelope to form a seal, leading-inconductors secured to the wall of each of said cylindrical members andextending exteriorly of said envelope, and electrodes within saidenvelope between which a discharge occurs when supplied with electricalenergy and subjectable to extremely high temperatures, each of saidelectrodes having its ends connected to the periphery of the respectivecylindrical member and extending a substantial distance on the surfacethereof in the direction of the longitudinal axis of said cylinder toform a support for each of said electrodes directly from said seals.

3. The combination of a discharge device provided with an elongatedenvelope of vitreous material, a leading-in conductor disposed atopposite ends of said elongated envelope comprising substantially acylindrical member formed of metal foil having a core of the samevitreous material as said envelope to form a fused seal integral withthe latter, a leading-in-conductor secured to the wall of saidcylindrical member and extending exteriorly of said envelope, and anelectrode disposed at each end of said envelope between which adischarge occurs and subjectable to extremely high temperatures, andeach of said electrodes having their ends connected to the periphery ofthe respective cylindrical member and extending a substantial distance0n the outer surface thereof in the direction of the longitudinal axisof said cylindrical member to form a support for each of said electrodesdirectly from said seal.

4. A current conducting seal for an electric stantial distance on theouter surface in the direction of the longitudinal axis of saidcylindrical member, and a wire having a bifurcated end portion connectedto the periphery of said cylindrical member and extending a substantialdistance on the outer surface thereof and extending exteriorly of theenvelope of said discharge device.

5. A current conducting seal for an electric discharge device having avitreous envelope comprising a substantially cylindrical member of metalfoil having a longitudinal slot therein and provided with a core ofvitreous material of the same composition as the envelope of saiddischarge device and readily fusible with the latter to entirelysurround the cylindrical member and form an integral vacuum tight seal,an electrode having its ends connected to the periphery of saidcylindrical member and extending a substantial distance on the outersurface in the direction of the longitudinal axis of said cylindricalmember, and a wire having a bifurcated end portion connected to theperiphery of said cylindrical member and extending a substantialdistance on the outer surface thereof, and the remaining portion of saidWire being coaxially disposed relative to the longitudinal axis of saidcylindrical member and extending exteriorly of the envelope of saiddevice.

JOHN WESLEY MARDEN. GEORGE MEIS'I'ER.

